commsec order cancel problem

This morning I ordered PRRO to buy @ 5.3c and i see the order is not executing ! I then cancel the order and waited several minues (near 10 min) and refresehd but it showed cancel pending. I also got my cancel ref. no. But soon after that I see order is executed. My question, I could cancel the order , how was it executed. Can I put a cancel order now which was executed yesterday is my question !

Commsec upgraded their system this weekend and this is the output!

My cancel order details:

Order Details
Order Type: Buy
ASX Code: PRRO (PRIMA BIOMED LTD OPT DEC11 (OPTION EXPIRING 31-DEC-2011))
Price: $0.053
Quantity Ordered: 100000
Quantity Outstanding: 100000
Quantity Executed: 0
Order Style: Default Expiry
Expiry Date: 27/08/2009
Status: Cancel Pending
Reference Number: N43620431


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Order History

30 Jul 2009 10:11:Instruction: New Buy 100000 PRRO @ $0.053

30 Jul 2009 10:14:Instruction: Cancel Buy 100000 PRRO @ $0.053